1. Field of the Invention
This invention relates to sound operated electrical control devices and, more particularly, to a device for converting selected acoustical sounds into predetermined electrical outputs to actuate means for energizing or de-energizing remote electrical systems.
2. Description of the Prior Art
Sophisticated sound activated electrical control systems are generally based on discriminating between "voiced" sounds and "frictional" sounds or differentiating the frequency distribution between relatively distinctive voiced sounds.
Representative of the former system is U.S. Pat. No. 3,286,031 which utilizes the asymmetric amplitude character of the electrical voice signal envelope not found in frictional sounds. Low-pass and high-pass filters are used in conjunction with an amplitude peak detector to differentiate between the voiced and frictional sounds.
U.S. Pat. No. 3,688,126 is illustrative of the latter system wherein the frequency distribution between the voiced word "yes" and "no" are differentiated. A frequency analyzer and integration circuitry are utilized with flip-flops to form the voice-operated switch.
The above systems are purportedly more reliable than systems based on differences in acoustical input power because of the possibility of occasional loud ambient noise causing unintentional actuation. However, the extensive circuitry and numerous components required in the above systems inherently render them expensive to construct and maintain as a reliable unit. It will also be appreciated that there is a long felt need for sound actuated devices in hospitals, convalescent homes, factories and laboratories which can be produced on an economical large volume basis. Due to the complicated nature of prior art devices, the high cost of manufacture has obviated fulfilling such needs.